1. Field of the Invention
The present invention relates to an apparatus for measuring a brain local activity, and in particular to an apparatus for measuring or estimating a degree of neuronal impairment (diminishment) state in brain cortex such as a senile dementia disorder.
2. Description of the Related Art
With respect to senile dementia, it is statistically said that about 30% of nonagenarians are in dementia. This senile dementia is becoming a serious problem for the coming aging society.
Accordingly, such a dementia disorder should be preferably found as early as possible and treated before it results in a serious state. As an apparatus for measuring (estimating) a degree of the dementia disorder, an apparatus for measuring a brain local activity has been already proposed comprising: a plurality of sensors mounted on a head of a subject for measuring scalp potentials or magnetic fields of the subject; a computing unit for converting alpha wave components of output signals of the sensors into numerical data to determine a dipolarity at each sampling, for determining mean values of squared errors, within a fixed time interval, between a scalp potential or a magnetic field by an equivalent dipole at a dipolarity peak emergence time and the measured scalp potentials or magnetic fields or variances of the squared errors from the mean values for the sensors, and for mapping a contour concerning a distribution of the mean values or the variances on a scalp or a brain surface corresponding thereto; and an output unit for outputting a contour map (see e.g. patent document 1).
[Patent document 1] Japanese patent No. 3581361
The above-mentioned patent document 1 detects a functional impairment of neurons in some part of a brain by analyzing a scalp potential distribution of alpha waves, so that there have been following problems:    a) A large number of persons do not show alpha waves    b) The alpha waves are restrained in an eye-opening state, which is extremely unstable;    c) The alpha waves are highly affected by a state of mind;    d) Localization of a brain functional impairment degree only by the alpha waves does not properly coincide with a cerebral blood flow diminished part by SPECT (Single Photon Emission Computing Tomography).
Namely, since the patent document 1 consistently carries out a measurement based on the alpha waves, there have been problems that a functional impairment part of neurons can not be detected, a type and a degree of a brain disorder are unclear, and a part in which the neuronal function has recovered by various treatments is unclear.